The invention relates to a method for the simultaneous, continuous interfiber bonding and coating of a nonwoven fabric with a bonding agent and an adhesive composition.
In European Patent Application No. 12776, a method is described for interfiber bonding of a nonwoven fabric by application of a UV-cross linkable bonding agent and subsequent irradiation with a high pressure mercury lamp. The application of an adhesive composition is not discussed.
A method for applying bonding agent and adhesive to a fabric is described in Japanese Provisional Patent No. 1667/1975. According to this patent, the bonding agent and the adhesive compositions are simultaneously applied while the fabric material is passed through a pair of gravure or screen cylinders. The resulting printing patterns obtained on both sides of the material are identical.
The known methods for applying bonding agent and adhesive composition simultaneously to the top and bottom sides of the fabric use an identical printing technique for the treatment of both sides. Relatively equal compression forces are produced by this technique, however, and it is extremely difficult to obtain different penetration levels of the bonding agent and adhesive composition. Relative variation of the size of the applied printed patterns is not possible, and higher printing speeds can lead, especially in the treatment of an unbonded nap of nonwoven fiber fabrics, to a smudged printing pattern and undefined properties of the fabric obtained.
These methods, therefore, do not comport with the intended purpose of the two applied substances. The primary purpose of a bonding agent is to bind the fibers of a nonwoven fabric to each other and to give it strength. Strength is increased by binding more fibers together. It is therefore desirable that the bonding agent penetrate into the interior of the treated nonwoven fabric and, after its incorporation, it should be substantially uniformly distributed over the entire cross-section.
In contrast, the adhesive compositions are applied to the surface of fabric material in order to enable bonding to another material. Typical adhesive compositions are thermoplastic substances, and the activation is accomplished through application of pressure and heat, for instance, with an iron. The adhesive composition should not penetrate into the interior of the fabric during the ironing in order to be available in as concentrated a form as possible for the subsequent bonding to the other material.
Therefore, it is an object of the invention to develop a method for the simultaneous, continuous application of a bonding agent and an adhesive composition onto opposite sides of an unbonded nonwoven fabric so as to obtain a precise application pattern on both sides with penetration by the former and substantially none by the latter. Further objects include development of the ability to vary the specific quantity of agent or composition applied and an ability to use high operating speeds during application. This permits a reduction in the energy requirements of the process.